The field of the invention is the attraction of ocean fish to a planned location to enhance the return from fishing effort.
About two-thirds of the cost of wild fish caught in the open ocean is the effort of finding the fish and about one-third is the effort of catching and processing them. For this reason fishermen pride themselves on knowing where the fish congregate in order to gain a full trawl, long-line or net. One approach that fishermen take is scattering fish food or chum to attract migratory or pelagic fish, but this is expensive and short term. Fishermen have noticed that fish will congregate under floating patches of seaweed and under docks and floats. This has led to the use of fish attractive devices, called FADs. These are floats, about 100 square feet to 200 square feet in size, that provide a shadow in the ocean water to attract the fish, which then congregate there. These FADs are small and require deployment and retrieval by the fishing vessels.
A large FAD (Fish Attractive Device) can be achieved at low cost by fertilizing the ocean surface to create a bloom of phytoplankton of sufficient density to form a patch. These biological FAD patches may exist for about 1 to 2 months after creation.
A method of increasing the fish catch in the ocean may comprise the following steps: (1) testing an area of the surface of the ocean to confirm that each macronutrient is present at a first predetermined level that allows for the production of phytoplankton; (2) testing the area of the surface of the ocean to confirm that a first micronutrient is present at a second predetermined level which limits the production of phytoplankton; (3) testing the area of the surface of the ocean to confirm that the rate of diffusion is at a third predetermined level which allows for the production of a patch of phytoplankton; (4) applying a fertilizer comprising the limiting micronutrient to create a patch of phytoplankton in the area of the surface of the ocean; and (5) harvesting the fish underneath and in the area of the patch.
A method of creating an FAD in the ocean may be achieved by the following steps: (1) testing the water at the ocean surface to determine the nutrients that are missing or are in a limiting concentration; (2) applying a fertilizer that releases an appropriate amount of these missing or limiting nutrients in a form that remains available to the phytoplankton such that these nutrient do not leave the photic zone by precipitation to any appreciable extent; and (3) selecting an area of the ocean which has waters that do not rapidly mix either horizontally or vertically (the water should have a diffusion coefficient less that 6.7 square miles per day) and be in the general area of pelagic and migratory fish patterns. In oceans, sufficient sunlight to support the process of photosynthesis is present in only the about 100 to about 200 meters of water beneath the surface of the ocean. The term photic zone may be used to describe this area, where all of the ocean""s photosynthesis takes place. Below the photic zone, there is the aphotic zone where there is insufficient light to support photosynthesis.
A nutrient is present at a limiting concentration if the production of phytoplankton is reduced to a significant extent by the level of that nutrient in the ocean water. An appropriate amount of such a limiting nutrient is an amount needed to raise the concentration of that nutrient in the photic zone so that the bloom of phytoplankton is no longer reduced to a significant extent by the concentration of that nutrient. In most of the ocean the limiting nutrient is iron. Thus, a preferred fertilizer of the present invention comprises chelated iron. The preferred chelates include lignin acid sulfonate.
The diffusion rate varies in the ocean water. The method is preferably carried out in an area of the ocean that does not mix so rapidly that the patch is dispersed before the fish are attracted.
An appropriate amount of a missing micronutrient is an amount that permits the phytoplankton to bloom to a substantially greater extent as permitted by the macronutrients in the ocean water, which are usually nitrate, phosphate and silicate.
The number of fish that aggregate per unit of patch area may be used to determine optimum patch size. If the patch exceeds the optimum, then the return per unit of patch area will decrease, and if too small then the mixing and diffusion will obliterate the patch before the fish can aggregate to a significant extent.
The environmental effects of the fertilized patches are expected to be benign. Chelated iron is used as a dietary supplement for people and as a terrestrial iron fertilizer for gardens. Phytoplankton secrete chelating agents into the ocean water in an effort to keep iron available for making the chlorophyll required for plant growth. The chelated iron has a lifetime in the ocean water of about 40 days so the patch does not have to be revisited. Instead, a new patch may be created in a new location.